In article transport facilities such as one described above, articles are transported by traveling article transport vehicles. There are article transport vehicles that are of a hoist type that travel in the ceiling area of work space, and that are of a carriage type that travel on the floor area of the work space.
An example of an article transport facility disclosed in JP Publication of Application No. 2011-116313 (Patent Document 1) is one including an article transport vehicle of the hoist type that travels in a ceiling area of work space. In the example in Patent Document 1, the article transport vehicle travels in a ceiling area of a clean room, and transports, as an article, a container for storing substrates, such as silicon substrates.
More specifically, travel rails for the article transport vehicle are provided in the ceiling area of a clean room so as to extend along a predetermined travel path extending along, or by way of, substrate processing devices. The article transport vehicle is configured to travel along the predetermined travel path by obtaining propelling force by drivingly rotating travel wheels, which function as propelling rotatable members, with the travel wheels kept in contact with travel surfaces of the travel rails, which function as contact portions.
Incidentally, the article transport vehicle of Patent Document 1 includes an article grip portion which can be moved vertically. When transferring an article to a carry-in-and-out portion of a substrate processing device, the article transport vehicle vertically moves the article grip portion with the article transport vehicle stopped at a stop location that corresponds to the carry-in-and-out portion of the substrate processing device.
The article transport facility of Patent Document 1 is configured such that the article transport vehicle travels by means of the propelling force obtained by drivingly rotating the propelling rotatable members over the entire range of the predetermined travel path. There may be a section in the predetermined travel path in which it is desired to cause the article transport vehicle to travel faster than in other sections.
More particularly, for example, with space inside each of a plurality of operations buildings that are spaced apart from each other being defined as a work zone, the predetermined travel path may include work zone travel path portions for transporting articles within each of a plurality of work zones, and connecting travel path portions for connecting work zone travel path portions for transporting articles among the plurality of work zones. In such case, for example, the travel speed of the article transport vehicle when traveling in a connecting travel path portion is desired to be greater than the travel speed of the article transport vehicle when travelling in a work zone travel path portion. Thus, there may be a section in the predetermined travel path in which it is desired to cause the article transport vehicle to travel faster than in other sections.
The following are the reasons why the travel speed of the article transport vehicle when traveling in a connecting travel path portion is desired to be greater than the travel speed of the article transport vehicle when travelling in a work zone travel path portion. An article transport vehicle can travel continuously without stopping in a connecting travel path portion, and the connecting travel path portion can be constructed to extend straight, for example, to allow article transport vehicles to travel at higher speeds. Thus, it is desirable to cause the article transport vehicles to travel at higher speeds in such connecting travel path portions in order to improve article transporting efficiency.
In contrast, an article transport vehicle is stopped at a number of stop locations to transfer an article in a work zone travel path portion. And work zone travel path portions are installed with curved path portions in many cases, making it difficult to cause the article transport vehicle to travel at higher speeds. For these reasons, the travel speed of the article transport vehicle when travelling in a work zone travel path portion is not required to be greater than the travel speed of the article transport vehicle when traveling in a connecting travel path portion.
In order to satisfy such requirement, an article transport vehicle may be provided with a large high-output electric motor that drivingly rotates propelling rotatable members at higher speeds so that the article transport vehicle can travel at sufficiently higher speeds by means of the propelling force obtained by drivingly rotating the propelling rotatable members with the large motor. In this case, however, because the article transport vehicle is provided with a large and expensive electric motor, there is a disadvantage that the entire facility becomes expensive, which makes this a difficult option to implement.
More specifically, an article transport facility commonly has many article transport vehicles. And the entire facility becomes expensive if each of the many article transport vehicles is equipped with such an expensive electric motor.
If the article transport vehicle is of the hoist type where the article transport vehicle travels in the ceiling portion, and if the weight of the article transport vehicle is increased by the provision of a large electric motor, then the travel rails for the article transport vehicle need to be configured to have sufficient strength that would withstand the large weight which is the sum total of the weight of the article transport vehicle whose weight has increased as the result of providing it with the large electric motor, and the weight of the article transported by the article transport vehicle. Thus, there is also a disadvantage that the entire facility becomes expensive as the result of the increased installation cost of the travel rails.
Incidentally, there may be a section in the predetermined travel path in which it is desired to cause the article transport vehicle to travel faster than in other sections in an existing article transport facility as well, in order to improve article transporting efficiency. In such cases, it is difficult in practice to convert existing article transport vehicles so that they can travel at higher speeds. Thus, it may be impossible to cause the article transport vehicle to travel at higher speeds in existing article transport facilities.